Disproportionation & Electrode Potential (Edexcel A Level Chemistry): Revision Note

Disproportionation & Electrode Potential

• A disproportionation reaction is where one element in a chemical is simultaneously reduced and oxidised, e.g.

2Cu⁺ (aq) → Cu²⁺ (aq) + Cu (s)

• Standard electrode potentials can be used to explain disproportionation reactions

1. Cu²⁺ (aq) + e^– ⇌ Cu⁺ (aq)   E^⦵ = +0.15 V

2. Cu⁺ (aq) + e^– ⇌ Cu (s)  E^⦵ = +0.52 V

• The electrode potential value for equation 1 is more negative, therefore, this reaction will be the oxidation reaction and proceed to the left

• The electrode potential value for equation 2 is more positive, therefore, this reaction will be the reduction reaction and proceed to the right

  • You now have:

Cu⁺ (aq) ⇌ Cu²⁺ (aq) + e^– 

    Cu⁺ (aq) + e^– ⇌ Cu (s)  

• Combining these two equations agrees that the overall equation is possible 

2Cu⁺ (aq) → Cu²⁺ (aq) + Cu (s)

• Copper is oxidised from +1 to +2 and reduced from +1 to 0, so Cu⁺ is both oxidised and reduced

• E^⦵_cell = E^⦵_reduction − E^⦵_oxidation = (+0.52) − (+0.15) = +0.37 V

• E^⦵_cell is positive, so the disproportionation of Cu⁺ (aq) is feasible